Isomerization catalysts comprising a Group VIII noble metal and a hydrocarbon-substituted aluminum compound on an alumina carrier are known in the art, as are processes for the preparation thereof.
GB Patent 1 432 639 describes a process for preparing an isomerization catalyst of this description in which a composition comprising a Group VIII noble metal and alumina is contacted with a hydrocarbon-substituted aluminum halide, whereupon the resulting catalyst is used directly for isomerizing paraffins. GB Patent 952 348 describes a process for preparing an isomerization catalyst in which a composition comprising a Group VIII noble metal and alumina is contacted with a trialkyl aluminum compound, whereupon the whole is reacted with, e.g., a hydrogen halide at a temperature below 260.degree. C. This treatment may be followed by a further activation with hydrogen at a temperature below 371.degree. C. if so desired.
However, the catalysts described in these references fail to function in a satisfactory manner, and there is need for a catalyst of improved activity.
It has now been found that the activity of a catalyst composition comprising a Group VIII noble metal and a hydrocarbon-substituted aluminum compound on an alumina carrier containing up to 20 wt. % of other components can be enhanced by subjecting this composition to a high-temperature activation step in which the composition is contacted with a hydrogen-containing gas at a temperature of 500.degree. C. or higher. In this respect it should be taken into account that if the hydrocarbon-substituted aluminum compound is not a hydrocarbon-substituted aluminum halide, it will be necessary to contact the catalyst composition to be activated with a halogen compound, either prior to or during the activation step.